U.S. Pat. No. 4,111,812 teaches breaking oil/water/surfactant emulsions obtained from oil fields in which surfactants have been used in chemical flooding operations. The patent describes the use of an ultrafiltration process to break the emulsions and recover surfactants. The process is run at 1 to 10 atm. The patent states that the surfactant in the emulsion partitions between the permeated water phase and the retentate oil phase. To improve the degree of surfactant recovery the patent teaches that a co-surfactant is added to the emulsion before ultrafiltering.
U.S. Pat. No. 4,426,293 teaches that water/oil mixtures can be separated using ultrafiltration and that oil molecules can distort in shape and pass through holes smaller than the molecular size in the ultrafilter. That high pressure can force oil through a membrane which at lower pressures does not permeate oil, does not teach, suggest or imply that the selectivity of surfactant separation relative to water and oil can be controlled by proper choice of pressure and membrane pore size.